The specific goals of this proposal are to define the pathology, natural history and response to treatment of chronic myocarditis and intramyocardial small vessel disease in living patients. This will be done with the aid of endomyocardial biopsy which is part of the routine work-up at this institution for patients with cardiac disease of underminded etiology. Patients with chronic myocarditis and small vessel disease will be identified histologically and followed prospectively. One goal of this proposal is to characterize the relationship between these entities and the development of congestive cardiomyopathy. The endomyocardial biopsy will be used to prospectively study these diseases in living patients. Histologic, immunohistochemical and ultrastructural techniques will be used to study the natural history of chronic myocarditis. We will use hybridoma-derived monoclonal antibodies to identify specific subsets of immunocompetent cells in the myocardium of patients with myocarditis. Knowledge of the immunocompetent cells in myocarditis may lead to a more complete understanding of the pathogenesis of chronic myocarditis and will aid in the evaluation of immunosuppressive therapy in these patients. Histology, ultrastructure and quantitative morphometrics will be used to assess intramyocardial capillary basement membrane thickening and thickening of the arteriolar wall in patients with ischemic heart disease. We believe these two structural changes are associated with intramyocardial small vessel disease and are a factor in the development of cardiomyopathy. The relationship between intramyocardial small vessel disease and extramural coronary artery disease will be studied with reference to the use of the endomyocardial biopsy to evaluate medical and surgical therapy in patients with ischemic heart disease.